Instruction 3015-4148
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Functional Overview
General Description
Refrigerant monitors are specified to support compliance to federal, state and local safety codes governing
refrigerant emissions. Avoiding significant refrigerant loss reduces equipment replacement costs, maintains
equipment efficiency, promotes safety, and protects the environment.
The HGM300 provides for the continuous monitoring of refrigerant gas levels in up to 16 separate test zones.
The instrument is easily programmed to monitor a variety of gasses and independent leak (small), spill
(medium), and evacuation (large) levels may be designated for each zone. The instrument also retains a log
of previous readings that can be easily accessed for analysis.
An audible alarm and large LED indicators are provided to signal alarm conditions, and relay contacts are
provided for connection of external alarm devices. The system also includes two (2) 4-20mA current loop
interfaces (optional) for connection to external devices.
The HGM300 requires only minor periodic maintenance such as the occasional replacement of filters. The
instrument incorporates active diagnostics that continuously monitor the system for proper operation. An LED
indicator is provided to indicate system malfunctions and fault codes are generated that enable the user to
identify the source of the fault.
Communication Options
The HGM300 features full two-way communications via an RS-485 interface. MODBUS RTU is the
communication protocol standard. The instrument can be connected directly to a Building Management
System or it may be operated as a stand-alone system using the Bacharach Display Module
(P/N 3015-2875).
An RS-232C port is also provided for connection to a PC. This enables the HGM300 to be setup from a
personal computer.
Please refer to the Appendix for a more complete discussion of communication protocols.
Understanding Monitoring Levels
Effective use of this instrument requires an understanding of what constitutes reasonable alarm set points for
the type of gasses being monitored. All AC&R systems leak some refrigerant. In a good “tight” installation
these background levels will be acceptably low and often do not require corrective action. You can reduce
nuisance alarms and needless service calls if the alarm levels are set at practical limits.
Refrigerant manufacturers define allowable exposure levels and threshold limit values in units of parts per
million (PPM). Bacharach has developed recommended monitoring levels based on compliance to ANSI/BSR
ASHRE 15-1994 and ASHRAE Safety Code 34-1992. These reference levels are listed in the Appendix.
Setting the unit at these recommended alarm levels will satisfy the needs of most users. However, the PPM
levels generated by system leaks into the environment are greatly influenced by the volume of air in the
sampling area, air circulation, size of the leak, distance to the monitoring point, and a host of other variables.
In some cases the set points may need to be adjusted either up or down to achieve effective monitoring.
Suggested Location of Sampling Points
At the point of a refrigerant leak the gas is nearly pure. As the refrigerant is dispersed into the air, the gas
molecules diffuse causing a dilution of the original concentration. The HGM300 measures the refrigerant
concentration at the precise point the sample is collected. Therefore, if the termination of the collection line is
not at the exact point of the refrigerant leak, then the unit will read a diluted mixture of the refrigerant gas
and air.
It should also be noted that refrigerant gas is heavier than air and tends to collect below the point of a leak.
Therefore samples taken near the floor will have a greater concentration of gas than those collected above
the source of a leak will. Consequently, sampling points should ideally be located as close as possible to the
source of potential leaks. Line-end filters should be mounted 12" to18" above the floor. If this is impractical,
then the alarm set points should be adjusted for that zone to compensate for the dilution of the refrigerant gas.
DO NOT plug any of the zones.
Plugging a zone will give the monitor a false indication during start up.
